1. Field of the Invention
The present invention refers to an electric motor comprising a stator with an internal permanent magnet and a tubular magnetic return sleeve surrounding said permanent magnet whereby an annular air gap is formed therebetween, said magnetic return sleeve being held at its axial and radial positions relative to said permanent magnet by a frame of plastic material injected around these two components and being connected to said permanent magnet by said plastic frame.
2. Description of the Prior Art
Such motors are known as d.c. motors having a permanent magnet and an iron-free rotor. In the prior art, the magnetic return sleeve is connected to the permanent magnet by providing said magnetic return sleeve, which has been produced by turning, with suitable annular grooves or annular webs which can be surrounded by the plastic material by injection moulding. For this purpose, the permanent magnet blank, which has not yet been magnetized, and the magnetic return sleeve are positioned in an injection mould and, subsequently, the connection is established by injecting plastic material which then surrounds these components in the desired manner. On the whole, it proved to be useful to position these components relative to one another and to anchor them on one another in the manner described hereinbefore. Attempts are, however, made to find less expensive solutions in the field of connection technology.
Hence, it is the object of the present invention to provide a d.c. motor of the type described at the beginning, which offers a positioning and anchoring possibility of sufficient stability which is less difficult to produce.